Cranial surgery requires access to a specific area of the brain. To gain such access, the surgeon must form a brain access flap in the cranium of the patient. Typically, the surgeon drills three spaced burr holes through the cranium at the apexes of an imaginary triangularly shaped access area. Because of the curvature of the cranium, the access flap is not a true planar triangle. The flap also may not be triangular but may be rectangular or be other polygonal or irregular shapes. If the access flap has more than three apexes, the surgeon usually drills a burr hole at each apex. Some surgeons use a single burr hole.
After cutting the burr holes, the surgeon then cuts though the cranium using a high-speed cutting tool. The tool has a guard that is inserted in the burr hole under the bone and above the dura. When the surgeon uses multiple burr holes, the cuts extend between the burr holes to form a removable cranial flap. Surgeons using a single burr hole cut the flap freehand in a pattern out from the hole and then returning to the hole. Once the surgeon has formed the flap, he or she carefully removes the flap to provide the necessary access to the brain.
These surgical procedures involve forming holes and gaps in the cranium to expose the brain. Therefore, each surgical operation requires a closing procedures to reattach the flap and to cover the burr holes. Burr hole covers that cover the burr hole and attach the flap are known. The Leibinger E-Z Flap is an example of such a burr hole cover. See also FIG. 1, which depicts a prior art burr hole cover. Although described in more detail in the "Detailed Description of the Exemplary Embodiments," prior art burr hole covers are described briefly here.
Burr hole covers consist of titanium, and many have a shape similar to some types of snow flakes. Some have a central body with five or six projecting arms. The distal ends of the arms usually have screw-receiving openings through which a cranial bone screw extends to attach the cover to the cranium. Some covers have very short arms extending from a larger central body. In others, screw-receiving openings are at the periphery of the central body so that the cover essentially has no arms. Often the arms or the screw-receiving openings are asymmetrically spaced. The asymmetry allows the surgeon to rotate the cover until all screw holes can be over good bone. The cover also has openings that speed healing.
Cranial surgery procedures sometimes require the monitoring of intra-cranial pressures following surgery. In this regard, the surgeon typically inserts a monitoring tube next to the burr hole cover. This tube then remains in place for a sufficient period of time to complete the monitoring purposes. Monitoring typically takes from a few days to a week or more. When the patient no longer requires monitoring, the surgeon pulls the tube from the cranial cavity.
Both the insertion and removal of the tube presents challenges. The tube contains delicate fiber optics that can break easily if the tube bends during placement. The fiber optics also can break while the tube is in place over the course of several days. Also, the tube may snag and become stuck when removed. Therefore, having a new and improved burr hole cover that eases the placement, protection and removal of an intracranial monitoring tube safely and efficiently is highly desirable.
Another problem with prior art burr hole covers is that they project above the normal cranial surface. Though the projection may be slight, some patients can feel the cover through the scalp with their fingers. Making the transition from the cover to the cranial bone as gradual as possible is desirable.